1. Field of the Invention
This invention relates generally to a fluid control valve and, more particularly, to a balanced pulse-width modulated solenoid control valve.
2. Discussion of the Related Art
Most modern vehicles employ an automatic transmission controller which has several solenoid operated fluid control valves that are independently actuated to control the pressure of the transmission fluid in the vehicle""s transmission to operate various components of the transmission. For example, solenoid operated fluid control valves are known that use transmission fluid pressure to provide direct clutch control and line pressure control applications. The torque transmitted by a certain transmission clutch may be varied by varying the pressure of engagement between opposed clutch plates. Presently available transmission controllers can rapidly and precisely generate the desired electrical output signals used to operate the control valves in response to sensed vehicle operating conditions to provide this pressure.
One particular known solenoid valve used for this purpose is referred to as a balanced pulse-width modulated (PWM) solenoid valve, well known to those skilled in the art. Pulse-width modulated solenoid valves are used to supply a hydraulic control pressure that is a function of the duty cycle of a pulse-width modulated driver signal. A control pressure is provided that has a true linear relationship to variations in xe2x80x9con-timexe2x80x9d of the solenoid coil. A valve element that establishes a fluid connection of a control port to a pressure supply must be capable of rapid shifting movements in close synchronization with the energization and de-energization of the coil. In order to effectively provide this transmission control, the pulse-width modulated solenoid control valve should prevent the occurrence of oscillations due to the natural frequencies in the system, and smooth the pressure pulsations. The frequency of operation of the control valve is typically in the range of 12-100 Hz. Additionally, the valve seats must be capable of withstanding up to 1xc3x97109 switching operations at this frequency.
Most balanced PWM solenoid valves rely on the traditional spool valve design, known in the art, where the spool valve is slidably reciprocated within a valve body to move valve lands to selectively open and close hydraulic ports within the valve body. The amount of overlap between the spool valve lands and the valve body metering edges determines the degree of leakage through these ports when they are closed or sealed for a given spring pressure and coil current. Because these overlaps are necessarily small due to the need for high flow and good dynamic performance, and the coil currents and spring bias are usually low to decrease costs, the typical balanced PWM valve has relatively high leakage. Known designs try to minimize leakage by relying on expensive processing to form, for example, high precision spool valve outer diameters and valve body inner diameters to reduce radial clearance and compensate for the small overlap. Undesirably, this high precision processing results in higher production costs.
As the controllers become more sophisticated, the solenoid operated control valves must also include advancements and improvements over the state of the art. In this regard, it becomes important to increase the operating efficiency, reduce the cost, reduce the weight, reduce the complexity, etc. of the existing solenoid operated fluid control valves. Therefore, advancements in size, part reduction, component simplification, etc. of the control valves are advantageous.
It is an object of the present invention to provide a simplified solenoid control valve that is easy to manufacture, and has a reduced amount of leakage over those valves known in the art.
A solenoid control valve having a spool valve disposed within a valve body and an enlarged diameter sealing land which axially engages and seals against a valve stop. In the preferred embodiment, an upper surface of the sealing land seats against an upper valve stop when the spool valve is in a first sealing position and a lower surface of the sealing land seats against a lower valve stop when the spool valve in a second sealing position, to provide sealing pressure in an axial direction relative to the movement of the spool valve. The control valve includes an actuating portion having a coil and an armature. The armature is in direct contact with the spool valve, preferably through a stem that extends through the upper valve stop. When the coil is not energized, a valve spring biases the spool valve to seat against the upper valve stop so that a source pressure is provided at a control port. When the coil is energized, the armature moves the spool valve away from the upper valve stop against the bias of the valve spring and causes the sealing land to seat against the lower valve stop, sealing off the source pressure port. In this configuration, the control pressure is allowed to vent to exhaust.
Objects, features and advantages of the invention include providing a solenoid fluid control valve that is not dependent on close radial clearances between a spool valve and a valve body to provide a seal, enables axial engagement of a sealing surface and a valve stop to provide a seal, reduces leakage, reduces or eliminates expensive processing to form the spool valve and valve body, is more tolerant of contaminates, is readily adaptable to a wide range of fluid applications, is reliable, durable, of relatively simple design, and is less costly to manufacture and assemble.